This invention relates to sewing machines and, more particularly, to sewing machines having positional coordinates for successive stitch penetrations stored in a memory. Specifically, this invention relates to the alteration of such positional coordinates, under operator command, during the transmission of such coordinates to the stitch forming instrumentality positioners.
A system is disclosed in U.S. Pat. No. 4,016,821, issued on Apr. 12, 1977, wherein logic circuitry is used to select and release stitch information stored in a memory in timed relation with the operation of a sewing machine. Digital information from the memory is converted to positional analog signals which control closed loop servo systems including moving coil linear actuators directly controlling the position of conventional stitch forming instrumentalities of the sewing machine to reproduce a pattern of stitches corresponding to the selected stitch information. According to the system disclosed in the referenced patent, circuitry is provided which permits an operator to alter the stored bight and feed motions. Operator influenced means are effective to signal the logic circuitry to selectively apply a holding signal to an FET switch, maintaining the FET switch in the conductive state. Closing of this FET switch inserts the wiper of a potentiometer in bypass arrangement in the feedback circuit of an operational amplifier interposed between a digital to analog converter for feed or bight and, respectively, the feed or bight servo system. By changing the magnitude of the resistance in the feedback circuit of the operational amplifier, the gain of the amplifier may be selectively reduced, thereby controlling the signal to the feed or bight linear actuator for selective reduction of stitch length or pattern width, respectively.
While the system described above, as disclosed in the aforereferenced U.S. Patent, performs satisfactorily, the disclosed override control is an analog function added to a system which is otherwise digitally controlled. It is therefore an object of the present invention to provide digital override feed and bight controls for a stored pattern sewing machine.
When utilizing digital controls for the override functions, only a limited number of discrete override values are obtainable. This is an inherent limitation of a digital system. The limited set of discrete override values for one particular pattern may not be suitable as override values for another particular pattern. It is therefore another object of this invention to provide a plurality of sets of discrete override values, with the particular selected pattern determining which set of override values is utilized.
A limitation of the override system disclosed in the abovereferenced patent is that the only override control is the amount of reduction in gain which may be achieved. It is possible that rather than a reduction in gain, an increase in gain may be desired. For example, it may be desirable to increase the stitch length in a particular pattern above the stored stitch length. It is therefore a further object of this invention to provide an override amplification capability.